Preservative for wood



Patented May 8, 1934 UNITED STATES PRESERVATIVE FOR woon Karl Heinrich Wolman, Berlin-Grunewald,

Germany No Drawing.

Application July 2, 1929, Serial No.

37 5,600. In Germany July 20, 1928 4 Claims.

It has already been proposed to impregnate wood with aqueous solutions of protective substances, which consist of a mixture of soluble fluorine compounds and soluble arsenic com- 5 pounds, if desired with the addition of other antiseptic compounds or substances reducing the tendency of the wood to catch fire. These mixtures have proved valuable preservatives, because they are capable of protecting wood simultaneously from the attack of animal and vegetable pests, and have also the advantage that the fungicidal actions of the fluorine and arsenic compounds have a favourable effect one upon the other, so that the protective effect of the preservative substance considerably exceeds the sum effect of the fluorine and arsenic compounds con tained therein..

It has been found that it is advisable in many cases, to employ arsenic and fluorine compounds which are difficultly soluble in water instead of the arsenic or fluorine compounds comparatively readily-soluble in water. It is particularly advantageous to use these difficulty soluble compounds in cases in which there is any risk of a premature leaching out of the preservative introduced into the wood, by the admission of moisture, atmospheric deposits, soil water or the like. The preservative can beintroduced into the wood for instance by preparing a solution, which when the water evaporates, leaves behind in the impregnated wood a salt mixture, containing either the arsenic or the fluorine compounds or both in a difi'lcultly soluble form, if desired together with comparatively readily soluble fluorine or arsenic 5 compounds. In addition to these compounds there can naturally be present in the preservative other suitable fungicidal or insecticidal constituents or substances reducing the inflammability of the wood or iron protectives etc. Use can 40 also be made of 'difiicultly soluble compounds which under the .influence of chemical changes which occur in the used wood such as for example oxidation or formation of solvent substances by fungi, are converted into a more readily soluble form.

The method of procedure may also be such that the wood is impregnated successively with solutions of two readily soluble substances which when they combine in the wood enter into reaction, so that after the wood is dried, the desired mixture of substances which is wholly or partially diflicultly soluble, remains behind therein. The method described above can also be combined with this second method by the first or second 5 solution or both being so composed that when the wood is dried, they precipitate difiicultly soluble or practically insoluble compounds. When the wood is impregnated with two solutions it is advisable to introduce the first solution into the wood by an empty cell process, for instance by the so-called Riiping process, whereupon the second solution is applied by the so-called full cell process. The procedure may however also be such that the first solution is introduced into the wood by an empty cell process and then the wood is treated by the so-called immersion process by steeping it in the liquid concerned in open receptacles.

The Riiping process is a process according to which the wood in a closed container is subjected I0 first to an air pressure and then, while maintaining the air pressure, to a higher. liquid pressure, whereupon after drainingv oil the impregnating liquid, an evacuation of the impregnating vat is effected. The compressed air, which is contained 76 in the pores of the wood, forces the impregnating liquid out of the wood which is not absorbed by the fibers so that according to this process only the cell walls are substantially impregnated with the liquid while the cell empty spaces are not filled with the liquid. According to the socalled full cell process, the closed impregnating vat, wherein the wood is contained, is first evacuated and after the evacuation, the impregnating liquidis forced into the wood under high pressure. The result thereof is that after draining oil the impregnating liquid, not only the cell walls of the wood are impregnated but also the cells empty spaces are filled with the impregnating liquid.

Example 1 The wood contained in aniron steeping vat is treated by the'so-called Riiping process with a 1% aqueous solution of zinc sulphate. In this process the wood is first of all exposed to an air pressure of for instance 3 atms. and then, while maintaining this pressure, the zinc sulphate solution is forced into the vat at a temperature 0 70 C. and a liquid pressure of '7 atms. This pressure is maintained for an hour, whereupon the liquid is drained ofi and the vat exhausted. The liquid emerging from the wood during the vacuum is drained off from the vat. It is then exhausted again. After a quarter of an'hours vacuum of at least 60 cms. an aqueous solution is introduced. into the vat, containing 0.5% sodium arsenite and 0.5% sodiumfiuoride. This liquidis forced into the vatuntil the pressure reaches 8 atms. This pressure is maintained for two hours, whereupon I10 the solution is drained ofi. The second solution is preferably also used in a hot state, for instance at a temperature of C.

Ewample 2 A salt mixture is prepared consisting of 20% sodium silicoflu'oride, 50% ammonium fluoride and 30% ammonium arsenate. A 1.5% aqueous solution of this is prepared, which is used at about 70 C. for impregnating the wood.

Example 3 A solution is prepared containing 5.0 parts cryst. copper sulphate, 8.0parts potassium sodium tartrate or so-called Seignette salt, 0.8 parts of sodium hydroxide in 500 parts water. Into this solution of about 70 C. temperature, the same quantity of a second solution is poured, which contains 5.0 parts of sodium fluoride, 2.0 parts of sodium arsenate, 1.0 part of potassium bichromate in 500 parts water. After mixing, the resulting solution is used to saturate the wood to be preserved, at about 70 C. by the full cell process. According to Hacks Chemical Dictionary, 1929 Edition, page 653, Seignette Salt is potassium sodium tartrate. Its formula is KNaC4H4Os+4H20.-

Emmple 4 A salt mixture 'is prepared consisting of 40% crystalline ferrous sulphate, 40 sodium fluoride, 10% arsenous acid, and 10% sodium bisulphate. A 2% solution of this is prepared while heating to not more than about 70 C. This solution is used for impregnating at a temperature also not exceeding 70 C.

The ferrous fluoride still present in a watersoluble form in the impregnating solution is converted when the impregnated wood is dried in the air, into the insoluble ferric cryolite. As a result of the hydrolysis of the iron cryolite, the velocity of which depends on the amount of intervening moisture, this compound is in the course of time re-converted into the soluble form in the wood.

My invention is not limited either to the use of the said substances or to the use of the method described. It relates broadly to means for preserving wood in aqueous solution with a content of fluorine compounds and arsenic compounds, which are present partially or wholly in a diflicultly soluble form, and to which other preferably more readily soluble protectives for wood can be added. By protectives for wood I mean in my application broadly all organic or inorganic substances which are capable of protecting wood against the attack of destructive fungi or insects, such as for instance termites, or against catching fire easily. The treatment of the wood with the preservatives according to my invention can be carried out in any desired manner, for instance by immersion, by impregnating in closed vats with the use of vacuum and pressure, according to an empty cell process or according to a full cell process.

What I claim is:-

1. A preservative for wood comprising 40% of crystalline sulphate of iron, 40% of sodium fluoride, 10% of arsenious acid and 10% of sodium bisulphite.

2. A preservative for wood comprising a solution of about 5 parts of crystalline copper sulfate, 8 parts of potassium sodium tartrate, 0.8 parts of sodium hydroxide in 500 parts of water, combined with a second solution in 500 parts of water of 5 parts of sodium fluoride, 2 parts of sodium arsenate and 1 part of bichromate of potassium.

3. A preservative for wood comprising a solution of 5 parts of crystallineferrous sulfate, 8 parts of potassium sodium tartrate, 0.8 parts of sodium hydroxide in 500 parts of water, combined with a second solution in 500 parts of water, of the following elements 5 parts of sodium fluoride, 2 parts sodium arsenate. and 1 part bichromate of potassium.

4. A preservative for wood comprising about 5 parts of crystalline copper sulfate, about 8 parts of potassium sodium tartrate, about 0.8 parts of sodium hydroxide, about 5 parts of sodium fluoride, about 2 parts of sodium arsenate and about 1 part of bichromate of potassium.

KARL HEINRICH WOLMAN. 

